This application claims the benefit of foreign priority Austrian Patent No. GM 723/99, filed Oct. 18, 1999.
The invention relates to a reciprocating machine with a friction bearing crank mechanism and a monitoring device for monitoring operating parameters of the friction bearings of the crank mechanism via at least one sensor associated with an evaluation device.
The crank mechanism, and in particular a crankshaft with connecting rods and pertaining bearings, is the mechanical hub of a reciprocating machine, such as a combustion engine or a compressor. The forces generated by all cylinders act on the crankshaft and its connecting rods and bearings, adding up to the total power output of the reciprocating machine. Therefore, diagnostic monitoring of the mechanism is particularly important. The invention is based on the premise that the beginning of a malfunction of individually disposed bearings or cylinders can be detected relatively isolated to a particular area.
It is known in the art that bearing defects can be detected by acoustic emission as the defect begins and increases in severity, particularly with high-frequency sound or ultrasound. See, for example Acoustic Emission Testing (Nondestructive Testing Handbook; Vol. 5) by Ronnie K. Miller, Paul McIntire, American Society for Nondestructive Testing, 1987; Diagnostic of sliding pairings by means of sound emission analysis, by A. Sturm, S. Kuhlemann, Mechanical Engineering Berling 34 (1985) 3, pages 129-132; Method and arrangement for detecting the cause of wearing symptoms in friction bearings, by A. Sturm et al., DE 41 23 576 A1 and DE 40 28 559 A1.
Sensors for structure-borne sound having a piezo-electrical measuring element are usually used for analyzing the effect of sound emission on solid body structures. However, resistive, capacitive, inductive, piezo-magnetic or optical sensors for structure-borne sound can also be used. A comparison is made between xe2x80x9cactivexe2x80x9d sensors, which require no auxiliary energy, and xe2x80x9cpassivexe2x80x9d sensors, which typically have to be supplied with electrical current or a stimulating light. Generally, the sensors are designed to be mountable on the structure surfaces and to receive structure-borne sound signals transmitted by the structure that reach the surface of the structure. There are, however, differences in the directional characteristics and in the modal sensitivity of the sensors. For example, a sensor can be designed to detect sound waves arriving radially versus axially with a longitudinal polarization or with a transversal polarization in a certain direction.
Errors in the operation of individual cylinders of an internal combustion engine, such as spark failure, knocking or differences in performance as compared to the performance of other cylinders, can be detected by a standard indication method based on measured gas pressures in the combustion chamber, and can also be used for individual cylinder control and monitoring.
Disadvantages of known methods and devices include the fact that the monitoring sensors usually have to be mounted on the exterior of the static structures, and therefore they are far removed from the hub of the mechanical action, i.e. the crankshaft and bearings. This results in inferior detection of beginning bearing defects and of errors in individual cylinder behavior.
Typical mounting of sound emission sensors on the exterior of components having structure-borne sound contact with the static exterior of bearing-structures causes a significant weakening in the signal and inferior localized sound source differentiation because of long sound paths relative to the wavelength of the high-frequency sounds. Both of the above effects result in an undesirable strength ratio between the wanted signal and the underground or interfering signal, and therefore in an inferior monitoring capability. Furthermore, such apparatus is only able to monitor the main bearings. The apparatus is not able to monitor the connecting rod bearings because the sound signals generated in the connecting rod bearings are weakened on their way to the sensors by the complex structures, joints and lubricating oil films of the crank mechanism and the housing. In some instances, the sound signals are weakened to the point of being virtually unusable.
Using combustion chamber pressure indicators for indicating the behavior of individual cylinders suffers from the extreme stress to which the sensors are subjected. At least the more cost-effective models typically do not provide adequate operational reliability and life-expectancy for monitoring functions, whereby alternative solutions need to be found.
An objective of the present invention is to overcome one or more of the aforementioned disadvantages of apparatus known in the art.
At least one sensor is positioned near the friction bearings to be monitored in the crank mechanism that moves relative to the machine""s housing, and the sensor""s connection with the evaluation device is guided, at least in part, via the crankshaft. The sensor is mounted in close proximity with the event to be monitored whereby it can be reliably located or detected and analyzed. By guiding the sensor signals out via the crankshaft, the structural element, which is mechanically highly stable, can be advantageously utilized and it can also be provided, for example, that individual signal lines are disposed in the lubricant bores, which are usually present in the crankshaft. This provides a fairly simple apparatus for reliably monitoring the friction bearings in addition to various measured variables that affect the crank mechanism.
In another embodiment of the present invention, a non-contact, preferably capacitive, transmission device is provided for feeding the sensor signals in and/or out of the connecting path that runs in or on the crankshaft, and the transmission device preferably operates without any auxiliary energy. In such embodiment, in the proximity of the connecting rod bearings on the connecting rod or the bearings associated therewith, for example, sensors can be provided which, via a capacitive transmission device or other medium transmit respective measuring signals to the crankshaft from where they are led to the outside, for example, via signal lines present in the lubricating oil bores, for example in the area of the toothed rim on the flywheel where, again via a non-contact transmission device, the output to the monitoring device can take place. This allows continuous monitoring of the connecting rod bearing, for example, where the respective measuring signals can be transmitted to the outside quasi continuously.
In another embodiment of the present invention at least one sensor is formed as a sensor for structure-borne sound for high-frequency sound waves which is advantageous for detecting the beginning of bearing damage.
In another embodiment of the invention, at least one sensor is designed for detecting low-frequency mechanical tensions and deformations and it is preferably disposed on the connecting rod bearing, thus allowing the connecting rod stress to be measured so as to provide a measure for the combustion chamber pressure in the pertaining cylinder, and thus allowing an evaluation of the individual cylinders of an internal combustion engine.
In a further embodiment of the invention, at least one sensor is designed for detecting low-frequency hydraulic lubricating oil pressure on at least one friction bearing of the crank mechanism. This allows both the lubricating oil pressure and the bearing play, and thus wear and tear associated therewith, to be monitored.
In another embodiment of the invention, at least one sensor is designed as a combination sensor for detecting various measured variables, both low-frequency and high-frequency, for joint transmission of the combined signal portions to the evaluation device.
It is particularly advantageous to design the monitoring sensor as a combination sensor for sensing ultrasound emission and for sensing lubricating oil pressure present on the bearing. In addition to the sensitivity for the low-frequency lubricating oil pressure and high-frequency sound emission of the adjacent bearings this is particularly advantageous for obtaining an additional high sensitivity for the sound emission of the lubricating oil which is cavitation-related, for example.
The high-frequency signal portion represents the received structure-borne sound and the low-frequency portion represents a further physical measured variable, and the two signal portions are combined and transmitted together. At the time they are evaluated, the two signal portions will be separated according to frequency and further processed. The low-frequency measured variable, for example, can characterize the forces transmitted by the connecting rod via the connecting rod bearing to the crankshaft, so that the measuring signal will indicate cylinder-specifically, among others, spark failure, knocking and any deviations in behavior as compared to the behavior of the remaining cylinders in an internal combustion engine. However, the low-frequency measured variable can also characterize the lubricating oil pressure present on the bearing, so that indications for an inadequate lubricating oil supply and/or lubrication can be detected in the measuring signal.
In another embodiment of the invention at least one sensor can be embedded in the solid body structure of the crank mechanism, preferably in the area of a friction bearing to be monitored, of a crank arm or the connecting rod. As a result of the relatively good sound transmission in the compact structure of the crankshaft, a sensor for structure-borne sound imbedded in the crankshaft will supply dominant signals originating from the closest sound sources. Therefore, one sensor may be sufficient for monitoring the adjacent main bearings and connecting rod bearings. By means of a correlative analysis of the signals of a sensor with the signals of at least a second sensor, such as the next closest sensor, which is mounted in the adjacent crank arm, for example, the sound source can be located. Thus, with this method, it is possible to differentiate which bearing the detected signals originate on, thereby advantageously saving some sensors and thus expenses, provided that the quality of the sound transmission in the crankshaft is adequate.
Accordingly, virtually no additional projecting parts are necessary on the crank mechanism. The sensor is fully encompassed by the measured object and its temperature, and thus it is well protected. Furthermore, the sensor can be optimally adapted to its measuring function. In case of a sensor for structure-borne sound, for example, a high sensitivity and selectivity can be achieved with regard to the longitudinal and transversal oriented sound waves present in the interior of the structure. Also, the style of the sensor and the method of mounting can be designed advantageously for a certain directional characteristic and mode sensitivity, thereby achieving an optimal utilization sensitivity and interfering signal suppression for the selected location where it is mounted and for the locations of interest of ultrasound emission.
A further embodiment is particularly advantageous in which a sensor is designed as a stopper for a boring on the crank arm leading to an exterior for supplying lubricating oil to the friction bearings. This allows a simple design and mounting of the monitoring sensor.
In another embodiment of the invention, at least one sensor is designed as a temperature sensor allowing both low and, when required, temporarily higher defined temperature monitoring of the bearings.
In a particularly advantageous embodiment of the invention electrical or electronic components are provided on the sensor, or at least near the location where the sensor is mounted on the crank mechanism for at least partial signal processing or handling, which components are connected both to the sensor and to the evaluation or monitoring device. Accordingly, at least a portion of signal processing can take place in direct proximity of the sensor with the known related advantages, which makes it considerably easier and less critical to further transmit the signal. For example, an electric filter connection for suppressing interfering frequency components of the sensor signal can also be integrated in the sensor itself, or a high-pass filtering for suppressing low-frequency signal components can take place directly at a sensor for structure-borne sound. On the other hand, with a sensor for a low-frequency measured variable, a low-pass filtering for suppressing high-frequency signal components can occur. In the case of a combination sensor, for example, the high-frequency and the low-frequency signals can be filtered by separate measuring elements, in one case high-pass filtered and in the other case low-pass filtered, before they are combined. Preferably, such electric filter connections contain only passive components (such as resistors, capacitors and inductors, for example) which will not require an additional voltage supply for the components.
In a further preferred embodiment of the invention, a common connection path to the evaluation device can be provided for transmitting the combined signals of multiple sensors during general monitoring wherein a diagnostic association of the signals to the signal-emitting sensor is not required.
In an advantageous embodiment of the invention the sensors themselves can comprise electrically active, preferably piezo-electrical, measuring elements with which the most varied measuring functions can reliably and accurately be carried out because such sensors are also relatively insensitive to high temperatures, vibrations and similar operating conditions.